Happy indeed is the man who follows not the counsel of the wicked--nor lingers in the way of sinners nor sits in the company of scorners--but whose delight is the law of the lord and who ponders his law day and night.
--Psalm 1

I guarantee that, if you spend three hours repeating the word "happy" with focused intention and attention, you will begin to feel it. It will take persistence--and you'll have to withdraw your attention from thoughts and feelings that aren't here and now--but the mantra will eventually identify with repetitive action, perhaps even breath and repetitive muscle movements. In hinduism, this is ajappa jappa--where the mantra prays itself and you sit back and watch. This is the space where "the Lord himself will fight for you, you have only to keep still." [bxA]

Psalm 1 says "happy is the man who avoids some stuff" then it goes into some detail. It says "be careful what you follow." Watch where you put your attention. It says "be careful what you linger on" Watch where you put your intention. It says be careful what you "sit in." Watch where you allow yourself to rest.

It might take a bit of inner hustle, but psychological health still rests on our delight being in the law of the Lord. Make your facade one of delight and then, with mantra, defend your rootedness in God's happiness. "Pondering God's law" should be done day and night. Whether we like it or not.
God is happy, but life isn't fair and it made resentment and remorse the shiniest of objects. God said "happy" and we followed our wickedness, lingered with our own sinfulness, sat in our own scorn. Tomorrow will have troubles of its own. Today, remain with God in happiness.

Ultimately this is a geography of the messianic secret. You wear facades in the name of dumb things all the time. Can you not wear a facade of quiet delight, so as to give yourself a guarded space where you can feel what resentment feels like, feel what remorse feels like? God said "happy indeed is the man" and you said BUT WHAT ABOUT MISERY too quickly. 

 Go into your room and shut the door.  Rest. Be rooted. Pray. The muscles of Joy have atrophied, and you do not know how to properly let go of anguish. "Happy." The Scriptures say "blessed are you who weep now, for you shall laugh." Even when things are a terrific mess, it's actually quite glorious. WOW!